Technical Abstract:
Brassicaceae seed meal soil amendments proved control of Rhizoctonia root rot, in part, through the proliferation of indigenous rhizosphere colonizing Streptomyces spp. Studies were conducted to assess the relative role of antibiosis and nitric oxide (NO) production in the capacity of Streptomyces strains to control R. solani AG-5. Among the four dozen isolates tested, there existed no clear association between capacity to suppress in vitro growth or produce NO and ability to suppress apple root infection by R. solani AG-5. Among those providing disease suppression, the NO-producing population provided greater disease control than the non-producing population, however severl exceptions were observed. Isolates of S. atratus (Antibiosis (Ab)-minus, NO-low),S.avidinii(Ab-minus,NO-high),and S.cirratus(Ab-low,NO-high) consistently suppressed apple root infection by R. solani AG-5. Surprisingly, R. solani root infection was significantly elevated in the presence of S. vinaceaus (Ab-monderate, NO-high). When co-inoculated with certain isolates of S. herbaricolor (Ab-high, NO-low) root infection was significantly elevated resulting in elicitation of novel leaf symptoms that were not observed on plants grown in soils infested with the pathogen alone. When examined individually, these same S. herbaricolor isolates induced leaf necrosis and inhibited apple seedling root development. Knowledge of these diverse interactions between the seed meal-modified Streptomyces population and apple roots will be of value in managing this population for suppression of R. solani AG-5.